Resistance unit.



- UNITED. STATES PATENT OFFICE.

ERNEST SCHATTNER, OF SCHENEOTADY, NEW YORK, ASSIGNOR TO GEN- ERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

RESISTANCE UNIT.

Specification of Letters Patent.

Patented Aug. 21, 1906.

Annil aflon filed March 31,1904. Serial No- 200.881.

To all. whomit may concern.-

Be it known that I, Eauas'r ScnA'r'rNna, a subject of the King of GreatBritain, residing at Schenectad county of Schenectady, State of New ork,have invented certain new and useful Improvements in Resistance Units,of which the following is a specification.

My invention relates to resistances for electrio circuits; and itsobjectis to rovide a novelform of resistance unit whic shall be simple,economical, and durable, which shall possess to a hi h degree thecharacteristics of reducing its 0 mic resistance as it becomes heated,and which shall possess such rate of decrease as may be desired;

Certain substances possess a negative temperature coefficientresistancethat is!' the decrease in ohmic resistance when heate Suchsubstances may be termed self-reducing resistances, particularly whenthe heat is the result of current traversing the substance. Certainsubstances possess this characteristic to such an extent that they maybe used in lace of hand-operated resistances in electnc circuits whereit is desirable that the resistance shall be great when current is firstap ually reduced. his is the case with the circuits of electricmotors,and the use of such a material as a starting resistance for an electricmotor is described in the application of O. P. Steinmetz for UnitedStates Letters Patent, Serial No. 44,067, filed January 21, 1901.

' Among the substances possessing negative temperature resistancecoefficients magnetite possesses the self-reducing characteristic to amarked degree and is thus particularly well suited for use as a startingresistance for electric motors and for similar pur oses. In startin anelectric motor it is desirable that the ful -load current should beadmitted to the motor at starting and that the resistance shoulddecrease at such a rate that the fullload current will continue to flowthrough the motor while the motor is accelerating from rest to fullspeed.

have discovered that pure magnetite reduces its resistance very rapidly,the result bein that when pure magnetite is used too smalI a current isadmitted to the motor for obtaining the maximum tor ue atstarting, or ifthe resistance is reduce sufliciently to represents a sel lied and shallthen be gradsecure proper starting-current the resistance of themagnetite decreases more rapidly than the counter electromotive force ofthe motor rises, and consequently too much current is admitted to themotor before it has reached full speed. I have found that the rate ofdecrease of resistance with magnetite may be varied by mixing with themagnetite other substances and that the rate of resistance decrease maybe predetermined by the amount and nature of the substance incororatedwith the magnetite. By this means am able to improve the characteristicsof a magnetite resistance. Furthermore, I when magnetite is made up instick form it cracks an disintegrates with fre uent applications ofcurrent, and consequentl makes bad contact and crumbles away. 11 orderto secure durability, this source of depreciation must be guardedagainst. I avoid the tendency to. disintegrate by forming the resistancefrom finely-pulverized magnetite and inclosing the same undercompression in an airtight receptacle.

In the accom anying drawings, Figure 1 reducing resistance unit formedin accordance with my invention, and Fi 2 is an explanatory diagram.

Iteferring first to Fig. 2, 1 represents a curve, showing the rate ofdecrease of pure magnetite when traversed by an electric current. Itwill be seen that the slo e of the curve isquite abrupt, andas a resu tthe resistance decreases faster than is desirable with a motor startingunder a load. Fig. 2 shows the rate of decrease of a resistance formedof magnetite mixed with a substance such as silicatefor example, mica.It will be seen that the slope of the curve is much less than that ofcurve 1, and as has been already said, the slope may be varied byvarying the amount of silicate mixed with the ma netite. I

n Fig. 1, A represents a metal tube lined with insulating material B,such as mica or asbestos. R represents the resistance material formed offinel -pulverized magnetite and finely-pulverize mica mixed in properproportions to secure the rate of decrease deslred. O 0 represent metalplugs, by means of which the resistance material ma be compressed withinthe tube and whic also act as terminals for the resistance unit. D Drepresent caps, tapped to be screwed onto the tube A and to force theplugs C inward, compressing the resistance material. Caps D areinsulated from the plug C by the mica washers E.

The process of manufacture is as follows: The magnetite :1 ml mica arefinely pulverized and mixed in the desired proportions. The insulatedtube is nearly filled with the mixture, the plugs (I are then insertedat the ends and forced inward by the caps D, thereby compressing thepowdered resistance material into a compact mass. The resistancematerial as thus mixed and compressed possesses a very high resistance,acting as an insulator. In order to give the resistance material itsproper characteristics, it is necessary that the tube be heated to atemperature at which'the mixture softens, the particles both of themagnetite and silicate uniting with each other producing a or stallinestructure. This process is aided y connecting the tube while it is beingbaked to a source of current, so that as soon as the resistance dropssufficiently the current will pass through the material and heat it upconsiderably more than the heat ap lied from outside does. After that itis a visable to let the unit cool and thereupon apply a sudden and heavycurrent for a few seconds, thereby effecting what I believe to becrystallization of the material. The character of the slope in the curveof resistance changes with reference to time may be altered by changingthe proportion of admixed materials. I have found that silicates, andespecially those of a heat refractory nature, are good for my purpose,but do not limit the use to any particular material. or com ound,though, as a rule, they should be condhctors of the second classthat isto say, they should be non-conductors when cold. Magnetite is aconductor of the first class and parsecond class. Therefore a compoundof two such substances may be made having a wide range of resistancecharacteristics, and my invention comprehends a wide field of selection.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is

1. As a new article of manufacture, a resistance consisting of aninsulated tube containing a mixture of a pulverized conductor of thefirst class with a pulverized conductor of the second class, therebyeffecting a resistance unit having a negative temperatureresistancecoefficient.

2. As a new article of manufacture, a selfreducing resistance unitconsisting of pulverized magnetite combined with a pulverized conductorof the second class.

3. As a new article of manufacture, a resistance unit consisting of apulverized material having a negative temperature-resistance coefficientintimatel combined with a flux.

4. As a new artic e of manufacture, a resistance unit consisting ofpulverized magnetite intimately combined with a pulverized silicate.

5. As a new article of manufacture, a resistance unit consisting of anair-ti ht insulated tube containing a compound aving a predeterminednegative resistance radient composed of two conductors having iflerenttemperature-resistance coefficients.

6. As a new article of manufacture, a resistance unit consisting of anair-tight insulated tube containin an intimately-related mixture of twocon uctors of the first and second class, respectivel 7. As a newarticle of manufacture, a resistance unit consisting of an insulatedtube containing a pulverized material having a negativetemperature-resistance coefficient combined with a flux and havingterminal plu s adapted to compress saidmaterial. anfair-tight insulatedcaps adapted to press said plugs upon said material.

8. As a new article of manufacture, a resistance unit consisting of aninsulated tube containin pulverized magnetite combined with a puTverizedsilicate and having terminal plugs adapted to compress said magnetite,and air-tight insulated caps adapted to press said plugs upon saidmagnetite.

9. As a new article of manufacture, a selfreducing resistance unitconsisting of pulverized magnetite combined with a flux.

10. As a new article of manufacture, a selfreducing resistance unitconsisting of pulverized magnetite combined with a pulverized silicate.

11. A self-reducing resistance material consisting of an agglomerate ofa conductor takes also of the nature of conductors of the having anegative temperature coefficient. and a refractory binder.

12. A self -reducing resistance material consisting of an agglomerate ofa conductor having a negative tem erature coefficient and a fluxinmaterial of liigher resistance.

13. A sel -reducin resistance material consistin of a partialfy-weldedagglomerate of a con uctor having a negative temperature coefficient,and a refractory material having a higher resistance.

14. A resistance material consisting of a partially-welded agglomerateof magnetite and a silicate.

In witness whereof I have hereunto set my hand this 29th day of March,1904.

ERNEST SCHATTNER.

Witnesses:

BENJAMIN B. HULL, HELEN ORFORD.

